Stress has become a major health concern amid increasing evidence it can cause changes in the gut and in the brain, which can in turn cause changes in behaviour.

In recent years there has been growing interest in the link between gut bacteria and stress-related disorders including anxiety, depression and irritable bowel syndrome.

Bacteria in the gut produce short-chain fatty acids (SCFAs), which are the main source of nutrition for cells in this region of the body. Foods such as grains, legumes and vegetables contain high levels of fibre and stimulate the production of these SCFAs.

In a study conducted by APC Microbiome Ireland attached to University College Cork and Teagasc Food Research Centre, researchers found there was decreased levels of stress and anxiety-like behaviour when SCFAs were introduced to the diet of mice.

Moreover, stress experienced over a prolonged period of time can affect the bowel by making the barrier between the inside of the gut and the rest of the body less effective and “leaky”.

Fibre helps to keep our digestive system healthy, reducing constipation and ensuring waste moves through the digestive tract more quickly

This means undigested food particles, bacteria and germs will pass through the leaky gut wall into the blood and cause persistent inflammation, according to one of the study’s authors, Prof John F Cryan of APC Microbiome. “Treating with the SCFAs can also reverse this ‘leakiness’,” he confirmed.

These results, published in the Journal of Physiology, provide new insights into mechanisms related to the impact of the gut bacteria on the brain and behaviour as well as gut health, Prof Cryan said. “Developing dietary treatments which target these bacteria will be important for treating stress-related disorders.”

Sugars and starch

Dietary fibre is made up of plant-based carbohydrates but are different to sugars and starch. It is not digested in the small intestine but reaches the large intestine or colon.

Including fibre-rich foods in a healthy balanced diet can improve weight maintenance. It can also counter risk of Cardiovascular disease (heart disease and stroke).

Fibre helps to keep our digestive system healthy, reducing constipation and ensuring waste moves through the digestive tract more quickly.

Including fibre-rich foods in a healthy balanced diet can improve weight maintenance. It can counter risk of Cardiovascular disease (heart disease and stroke); type 2 diabetes and bowel cancer – and help reduce cholesterol.

The UCC-Teagasc study, however, has confirmed likely additional benefits. It involved feeding mice the main SCFAs normally produced by the gut bacteria and then subjecting them to stress. Using behavioural tests the mice were assessed for anxiety and depressive-like behaviour, stress-responsiveness, cognition and sociability as well as how easily material passes through the gut.

It will be crucial that we look at whether short-chain fatty acids can ameliorate symptoms of stress-related disorders in humans

The exact mechanisms by which SCFAs facilitate their effect remain undetermined, the authors point out. SCFAs had no effect on an increase in body weight caused by stress therefore understanding why SCFAs only affect certain stress-induced effects will be important.

Prof Cryan added: “There is a growing recognition of the role of gut bacteria and the chemicals they make in the regulation of physiology and behaviour. The role of short-chain fatty acids in this process is poorly understood up until now. It will be crucial that we look at whether short-chain fatty acids can ameliorate symptoms of stress-related disorders in humans.”